Instead of using eight 500GB drives, you can opt for two 4TB WD Red Plus CMR drives, which would cost about 20 Euros per terabyte. These drives are brand new and come with a manufacturer's warranty.
If you plan to run the drives 24/7 in your NAS, you should also consider power consumption. HGST drives are power-hungry, idling at 5W or higher, whereas the WD40EFPX idles at 3.1W.
Eight HGST drives would consume 350 kWh per year, while two Red Plus drives would consume 54 kWh per year. I'm not sure about the efficiency of your NAS's PSU or your electricity costs, but saving 300-400 kWh or so per year would reduce your carbon footprint.
The NAS that I built in 2010 is a bit particular, it's made up of 3 nodes, each based on PPC40x, managing each a pair of disks in soft-RAID-1 (2xnode=2x3=6 disks), provided by a SiliconImage PCI chip. The nodes are controlled by a little SBC that is always online, consumes less than 5Watt, monitors the network traffic entering the NAS, if it notices a request for one of the three nodes that is offline (off), forces a softboot to the node, and in less than 12 seconds (bootstrap time) it satisfies the request. Similarly, if it sees no activity on a node within 40 minutes, it requests shutdown and turns off both the node and the hard disks connected to it.
Periodically (during night) also forces the bootstrap of the mediatower, and also organizes backups according to different levels. From daily backups, on DDS tape, to weekly backups on CDRW, to monthly backups on DVDRAM
. _______
| |
network === ctrl0 | _______
| | |A |--- sata.ch0----- hdd0
| === lan0 & uart0 === | node0 |--- sata.ch1----- hdd1
| | |_______|--- pata_ramdisk
| | |B |--- sata.ch0----- hdd2
| === lan1 & uart1 === | node1 |--- sata.ch1----- hdd3
| | |_______|--- pata_ramdisk
| | |C |--- sata.ch0----- hdd4
| === lan2 & uart2 === | node2 |--- sata.ch1----- hdd5
| | |_______|--- pata_ramdisk
| | _______________
| | |D |
| === lan3 =========== | media_tower |
| | | SCSI |
| | | + ramdisk |
| | | + media |
| | | + DVD-RAM |
| | | + CDRW650 |
| | | + DDS-4 |
| | |_______________|
|_______|
|
| uart4
___|__________
| |
| power unit |
| |
| |
| 12V,5V ---- group.A { node0, hdd0, hdd1 }
| 12V,5V ---- group.B { node1, hdd2, hdd3 }
| 12V,5V ---- group.C { node2, hdd4, hdd5 }
| 5V_TTL ---- group.D { media_tower } (ATX poweron)
|______________|
. ___________
| bay0 |
| ______|_
| | hdd0 |------ node0.sata.ch0
| |A_______|
| | hdd1 |------ node0.sata.ch1
| |A_______|
| | hdd2 |------ node1.sata.ch0
| |B_______|
|___________
| bay1 |
| ______|_
| | hdd3 |------ node1.sata.ch1
| |B_______|
| | hdd4 |------ node2.sata.ch0
| |C_______|
| | hdd5 |------ node2.sata.ch1
| |C_______|
|___________|
Through an internal 1000Mbps Ethernet line managed by a pair of Tulip chips (with dedicated network processors and queues, but limited to 20Mbyte/sec) the data flows from the disks of one of the three nodes to the SCSI ramdisk (8GB) of the mediatower, only then does the backup begin.
That NAS basically manages source archives in C and assembly, as well as vhdl, latek and txt files, vector files and some pictures, all things that never exceed 10Mbytes per file. I have developed software to track updates, so ONLY what ( = a project) has changed is backed up.
A 4GB DVDRAM fits perfectly into my monthly archives.
Made with late 90s and early 2000s tecnology, it had a troubled and controversial start, but this system has been working perfectly for 5 years now.
Why 3 sets of disks? Because things are compartmentalized into 3 big categories, which must NEVER be online at the same time, this is due to my paranoia.